In sprint athletics, the reaction time (RT; the time from the start signal to running onset) is one of the important factors determining performance. As RT is shorter, performance (i.e., total time) would be better. However, when RT is less than or equal to 100 ms, it is considered the premature start under the current regulations, leading to disqualification. Therefore, athletes need to decide on reaction strategy with the trade-off between gain (i.e., benefits for performance) and loss (i.e., disqualification). We examined how the level of advance in competition rounds (heats, semifinals, and finals) would affect RTs in the men's 100-m races at the four World Championships in Athletics held between 2011 and 2017. Results showed that the RTs in semifinals were the shortest among three competition rounds. We interpreted the results in terms of the optimization of energic costs on RT selection toward the final and/or the particular psychological states imposed by the demand level of performance in the final round.